Vol. 62 J. 



CHALK Aj*D BOULDER-CLAY NEAR ROYSTOjS". 



493 



a rock as Chalk. This, again, is only an hypothesis. I have studied 

 the places over which land-ice has passed in several parts of Europe 

 as well as in Canada, and have never been able to find any valid 

 evidence that it has, except perhaps under two very exceptional 

 circumstances, any power worth mention, either to excavate or to 

 break off large masses of rock. It can, no doubt, abrade considerably, 

 but the utmost thrusting work, so far as one can ascertain, which 

 it is capable of doing, is to push before it some morainic material 

 for a short distance, while it has often failed to produce any 

 appreciable disturbance, even on underlying stratified gravel. 

 Before, then, we invoke the shearing-thrust of an ice-sheet, to 

 explain certain relations of Chalk and Drift, we must first prove its 

 ability to accomplish such a task. 



(1) Pirmer>s-Cross Pit, Smith's End. 



Turning now to the particular sections, we will take the Pinner's- 

 Cross pit first, as its phenomena are the simpler. Here we find, as 

 Mr. Woodward describes, a few flint-bands, some of them very im- 

 perfectly developed, dipping at an angle of not less than 40° roughly 

 towards the north-west. Two at least of these seem somewhat 

 disturbed, as does the Chalk, for it is rather crushed and rubbly ; 

 that probably is a consequence of the movements which have bent 

 the Chalk, although it by no means follows that these were due to 

 the thrust of an ice-sheet. But I can add something to Mr. 

 Woodward's description : the Boulder- Clay is ' banked up against 

 the Chalk' 1 not only on its more southern, but also on its more 

 northern side. 2 Pig. 1 is a very rough sketch of what we saw. 



s.w. 



Pig. 1. — Pinner's- Gross Pit. 



N.E. 



>iHikilu1li^li.wW.4ii*|i 1 4kiii.KMi l dbn«M>(4|M> J in<4> M > , ' l ' , 'U(ii><iU(ia»i< 



A = Chalk-with-Flints. 



B = Boulder-Clay ; partly masked by talus of clay and soil. 

 [For minor details see Mr. Woodward's sketch, op. cit. fig. 3, p. 364.] 



The'Boulder-Clay occupies a hollow in the Chalk 3 ; the lower part 

 of this is masked by talus, but it is probably saucer-shaped ; its 

 breadth is about 5 yards, and the vertical height of the Clay exposed 



1 Quart. Journ. Greol. Soc. vol. lix (1903) p. 365. 



2 W. H. Penning, in Mem. Geol. Surv. ' The Geology of the N.W. Part 

 of Essex & the N.E. Part of Herts, &c.' (1878) p. 7, says that the Boulder- 

 Clay occupies a hollow in the Chalk. 



3 This disposes of Mr. Penning's difficulty referred to, op. cit. p. 372 

 Q. J. G. S. Xo. 247. 2 l 



